1. Field of the Invention
The present invention relates to a navigation apparatus for detecting a current location of a mobile body.
2. Description of the Related Art
One type of car navigation apparatus uses a recording medium such as CD-ROM which has map data stored therein. The map data includes road data which represent locations (or points) along streets/roads on a map by numbers. The car navigation apparatus detects a current location of the car and a moving direction of the car by using various sensors when the car is operated. At the same time, the car navigation apparatus reads a group of map data covering a certain area, which includes the current location of the car, from the recording medium to show a map of the area around the car in a display unit. The current location and moving direction of the car are both indicated automatically in the displayed map.
In the past, the navigation apparatus relies upon two navigation schemes. One scheme is self-contained navigation and the other scheme is GPS (global positioning system) navigation. The self-contained navigation utilizes self-contained sensors (e.g., acceleration sensor and angular velocity sensor) integrated in the navigation apparatus and does not receive any external support or information. The acceleration sensor and angular velocity sensor are used to detect (measure) navigation parameters such as acceleration and angular velocity of the car. The GPS navigation utilizes a plurality of artificial satellites which send measurement data (position data) to the navigation apparatus. The self-contained navigation has advantages and disadvantages, and the GPS navigation has advantages and disadvantages. In recent times, therefore, hybrid navigation is generally used, which combines (or compares) measurement data supplied from the self-contained navigation with measurement data supplied from the GPS navigation.
In order to improve detection accuracy of a current car location provided by the self-contained navigation or GPS navigation, a map matching technique is also employed. The map matching technique or process causes the detected car location to shift to the road of the map data (road corresponding to the map data) while the car is moving, if the detected car location deviates from the road of the map data. One example of such map matching process is disclosed in Japanese Patent Kokai No. 10-307037.
In the map matching process, if the current car location provided by the GPS navigation (referred to as xe2x80x9cGPS car locationxe2x80x9d) greatly deviates from the road of the map data, the navigation apparatus determines that the GPS car location is the true location of the car, and the display unit of the navigation apparatus displays a map in accordance with the GPS car location. However, when the car moves in a building such as a multi-story car park, the GPS car location suffers deteriorated accuracy because multipath affects the accuracy and/or the navigation apparatus cannot sufficiently receive measurement data (position data) from the artificial satellites. As a result, an accurate current location of the car is not obtained. In addition, if the map data does not have any data about the inside of the building, the map matching process cannot be performed even if the self-contained sensors provide the current car location. Such problems are also true to other types of navigation apparatus designed for other mobile bodies such as a human.
An object of the present invention is to provide a navigation apparatus that can determine a current location of a mobile body even when the mobile body moves in a building for which no map data is available.
According to one aspect of the present invention, there is provided a navigation apparatus comprising: a measurement unit for measuring a current moving direction and current location of a mobile body in accordance with navigation parameters of the mobile body; a presumption device for presuming a route pattern representing straight and curve ways along which the mobile body has moved, on the basis of the moving direction and current location of the mobile body measured by the measurement unit; a comparison unit for determining whether an actual route pattern determined in accordance with the moving direction and location of the mobile body measured by the measurement unit after the presumed route pattern is prepared matches the presumed route pattern; and a calibration unit for calibrating the current moving direction and current location of the mobile body measured by the measurement unit on the basis of the presumed route patter, when the comparison unit determines that the actual route pattern matches the presumed route pattern. A GPS device cannot provide accurate location data when the mobile body (e.g., a car) moves in a building having a roof (e.g., a multi-floor car park). Data about driveways in the car park may not be available in the navigation apparatus. The navigation apparatus can accurately determine the current location of the mobile body even if the mobile body moves in the roofed building and/or no driveway data is available.